When a patient's knee is severely damaged, such as by osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis, it may be desirous to repair and/or replace portions or the entirety of the knee with a total or partial knee replacement implant. Knee replacement surgery, also known as knee arthroplasty, can help relieve pain and restore function in injured and/or severely diseased knee joints, and is a well-tolerated and highly successful procedure. Where a total joint replacement is needed, it is often performed by a surgeon via an open procedure.
In an open procedure, the surgeon typically begins by making an incision through the various skin, fascia, and muscle layers to expose the knee joint and laterally dislocating the patella. The anterior cruciate ligament is often excised (if not already damaged or severed), and the surgeon will selectively sever or leave intact the posterior cruciate ligament—depending on the surgeon's preference and the condition of the PCL. Next, various surgical techniques are used to ablate, remove, shape or otherwise prepare the arthritic joint surfaces, and the tibia and femur are exposed for preparation and resection to accept various implant components.
It is well known in the art that knee arthroplasty involves the removal of one or more of the ligaments connecting the femur and the tibia. Often the normal function of one or more of the ligaments is severely compromised due to the deterioration or injury of the knee joint. One of the main purposes of a knee implant is to recreate the normal function of these removed ligaments. During this process, the ACL is almost always resected unless the surgeon chooses to use both a medial and lateral uni-compartment replacement. Meanwhile, the posterior cruciate ligament (PCL) is preserved in only about half of knee replacements performed.
Once the underlying bony anatomical support structures have been prepared, both the tibia and femur will typically receive an artificial joint component made of metal alloys, high-grade plastics and/or polymers to replace native anatomy and desirably function as a new knee joint. In the case of tibial implant components, the artificial joint can include a metal receiver tray that is firmly fixed to the tibia. In many cases, the tibial implant further includes a medical grade plastic insert (i.e. it may also be known as a “spacer” or “liner”) that can be attached to the tray and positioned between the femoral component(s) and the tibial tray to create a smooth gliding surface for articulation of the components. Such a system can also allow for inserts of multiple sizes and/or thicknesses, which facilitates in-situ balancing of the knee as well as allowing the placement of inserts of differing designs and/or shapes.
Various surgical procedures in the past have sought to retain connective knee tissues during joint repair and/or replacement, but such techniques and associated implant designs have not gained widespread clinical acceptance for a variety of reasons. See, for example, U.S. Pat. No. 4,207,627 to Cloutier, entitled “Knee Prosthesis” filed Jun. 17, 1980, and J. M. Cloutier, Results of Total Knee Arthroplasty With A Non-Constrained Prosthesis, 65 J. BONE JOINT SURG. AM. 906 (1983); J. M. Cloutier et al., Total Knee Arthroplasty with Retention of Both Cruciate Ligaments: A Nine to Eleven-Year Follow-Up Study, 81-A J. BONE JOINT SURG. AM. 697 (May 1999); Nowakowski A M, et al. Investigating the primary stability of the transversal support tibial plateau concept to retain both cruciate ligaments during total knee arthroplasty. J Appl Biomater Biomech. 2012 Mar. 30:0; and Ries, M D, Effect of ACL sacrifice, retention, or substitution on kinematics after TKA. Orthopedics. 2007 August; 30 (8 Suppl):74-6.
While the implantation of total knee implant components via open procedures is a well-accepted procedure that is well tolerated by patients and has a high success rate, surgeons often prefer to minimize the disruption and/or removal of hard and soft tissues except where absolutely necessary. For example, the use of minimally-invasive and/or less-invasive surgical procedures has become increasingly prevalent, as such procedures are often associated with faster patient healing times and less scarification of the patient's anatomy. Moreover, where portions of a patient's existing anatomy, such as an ACL or PCL, are substantially intact and/or functional in the damaged knee, many surgeons would prefer to maintain the integrity of these structures during the surgical implantation procedure, as such structures can greatly contribute to the ultimate stability and/or performance of the treated anatomy. Unfortunately, many current implant designs require the removal of such structures, even where such structures are fully functional, in order to accommodate the implant components.